arXiv subjects

R. Shyam

Publications and source records attributed to R. Shyam.

59 records · Page 4Linked to original sources

arXiv1997

Breakup probabilities and the optical potential in elastic deuteron scattering

We investigate the effect of the deuteron breakup on the optical potential for the elastic scattering of 56 MeV deuterons from $^{51}$V. The breakup probabilities calculated within the post-form distorted wave Born-approximation theory of breakup reactions are fitted to derive the contribution to the optical potential from the breakup channels. The breakup potentials are found to have large real as well as imaginary parts. Thus the dynamical polarization potential due to the breakup process is expected to modify strongly the real part of the optical potential calculated by the double folding model.

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arXiv1997

E2 component in subcoulomb breakup of ^{8}B

We calculate the angular distribution and total cross section of the ^{7}Be fragment emitted in the break up reaction of ^{8}B on ^{58}Ni and ^{208}Pb targets at the subCoulomb beam energy of 25.8 MeV, within the non-relativistic theory of Coulomb excitation with proper three-body kinematics. The relative contributions of the E1, E2 and M1 multipolarities to the cross sections are determined. The E2 component makes up about 65% and 40% of the ^{7}Be total cross section for the ^{58}Ni and ^{208}Pb targets respectively. We find that the extraction of the astrophysical S-factor, S_{17}(0), for the ^{7}Be(p,γ)^8B reaction at solar energies from the measurements of the cross sections of the ^{7}Be fragment in the Coulomb dissociation of ^{8}B at sub-Coulomb energies is still not free from the uncertainties of the E2 component.

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arXiv1996

$NN \to NN π$ reaction near threshold in a covariant one-boson-exchange model

We calculate the cross sections for the $p(p,nπ^{+})p$ and $p(p,pπ^{0})p$ reactions for proton beam energies near threshold in a covariant one-boson-exchange model, which incorporates the exchange of $π$, $ρ$, $σ$ and $ω$ mesons and treats both nucleon and delta isobar as intermediate states. The final state interaction effects have also been included. The $ω$ meson exchange is found to contribute significantly at these energies, which, along with other meson exchanges, provides an excellent agreement with the data. The cross sections at beam energies $\leq$ 300 MeV are almost free from the contributions of the $Δ$ isobar excitation.

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arXiv1996

Astrophysical S-factor of the $^7$Be($p,γ)^8$B reaction from Coulomb dissociation of $^8$B

The Coulomb dissociation method to obtain the astrophysical S-factor, $S_{17}(0)$, for the $^7$Be($p,γ)^8$B reaction at solar energies is investigated by analysing the recently measured data on the breakup reaction $^{208}$Pb$(^8$B,$^7$Be$~p)^{208}$Pb at 46.5 MeV/A beam energy. Breakup cross sections corresponding to E1, $E2$ and $M1$ transitions are calculated with a theory of Coulomb excitation that includes the effects of the Coulomb recoil as well as relativistic retardation. The interplay of nuclear and Coulomb contributions to the breakup process is studied by performing a full quantum mechanical calculation within the framework of the distorted-wave Born Approximation. In the kinematical regime of the present experiment, both nuclear as well as Coulomb-nuclear interference processes affect the pure Coulomb breakup cross sections very marginally. The $E2$ cross sections are strongly dependent on the model used to describe the structure of $^8$B. The value of $S_{17}(0)$ is deduced with and without $E2$ and $M1$ contributions added to the $E1$ cross sections and the results are discussed.

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arXiv1996

Pion production in proton-proton collisions in a covariant one boson exchange model

Motivated by the renewed interest in studying the pion production on nuclei with protons at few GeV incident energies, we investigate the pion production in proton-proton collisions over an energy range of 300 $MeV$ to 2 $GeV$. Starting from a realistic one-boson exchange model with parameters fitted to the amplitudes of the elastic nucleon-nucleon scattering, we perform fully covariant calculations for the total, double and triple differential cross-sections of the $p(p,nπ^+)p$ and $p(p,pπ^0)p$ reactions. The calculations incorporate the exchange of $π, ρ,ω$ and $σ$ mesons and treat nucleon and delta isobar as intermediate states. We obtain a reasonably good agreement with the experimental data in the entire range of beam energies. The form of the covariant delta propagator, the cut-off parameter for the $πNN$ and $πNΔ$ vertex form factors and the energy dependence of the delta isobar decay width is investigated.

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